A third-year fellow in pediatric gastroenterology, the applicant is interested in investigating intestinal gene regulation and developing the skills needed to attain a research career in academic medicine. The focus of the proposal is the intestinal bile acid binding protein (IBABP), a cytosolic protein believed to be involved in the bile acid (BA) absorption component of the enterohepatic circulation(EHC). This system maintain the BAP pool and thus is essential to lipid digestion and absorption. IBABP mRNA appears in rodents during the third postnatal week, a time coincident with the development of other parts of the EHC such as the apical transporter (ASBT) in the ileum and hepatic BA synthesis. This 5-yr award will provide enrichment of the applicant~s research career development through investigating the regulation of IBABP, an ileal marker which may provide insight into EHC and intestinal development. Initially, physiologic studies will determine the roles of luminal BA and gluco-corticoids (GC) on IBABP and ASBT mRNA levels in suckling rats. The possibility that the onset of IBABP and ASBT expression is controlled by an intrinsic timing mechanism will be examined by grafting fetal rat ileum s.c. into immune-deficient mice. In this model there is absence of luminal factors and the normal hormonal changes that occur in the developing rat. The contribution of transcriptional changes to the increased steady-state levels of IBABP mRNA during normal development and with BA and GC induction will be assessed by nuclear run-on assays. Subsequently, the intrinsic mechanism will be further defined at the cellular level with endoderm/mesenchyme dissociation and reassociations. Learning this technique in the laboratory of Dr. Michele Kedinger represents an invaluable opportunity to become adept at a skill which is not done in the United States. Finally, the rat IBABP gene will be isolated and characterized so that the cis-acting elements which mediate onto-genic regulation can be located through in vitro tranfections and in vivo transgenic mouse studies. Dr. Susan Henning's laboratory, whose primary focus is intestinal development, is an excellent environment in which to develop this proposal. Because BA absorption is immature in human infants as well as in suckling rats, this project may provide clinical application to managing neonates, especially those who are premature.